Union Pacific 4012
"Big Boy" 4012 on static display at Steamtown National Historic Site, August 2023
Type and origin Power type Steam Builder American Locomotive Company Serial number 69583 Build date November 1941
Specifications Configuration: ​  • Whyte 4-8-8-4  • UIC (2′D)D2′ h4 Gauge 4 ft 8+1⁄2 in (1,435 mm) Leading dia. 36 in (914 mm) Driver dia. 68 inches (170 cm) Trailing dia. 42 in (1,067 mm) Minimum curve 288 ft (88 m) radius/ 20° Wheelbase Locomotive: 72 ft 5.5 in (22.09 m) Overall: 117 ft 7 in (35.84 m) Length Locomotive: 85 ft 7.8 in (26.11 m) Overall: 132 ft 9+7⁄8 in (40.48 m) Width 11 ft (3.4 m) Height 16 ft 2+1⁄2 in (4.94 m) Axle load 67,500 lb (30,617 kilograms) Adhesive weight 540,000 lb (244,940 kilograms) Loco weight 762,000 lb (345,637 kilograms) Tender weight 342,200 lb (155,219 kilograms) (2/3 load) Total weight 1,250,000 lb (566,990 kilograms) Tender type 25-C Fuel type Coal Water cap. 24,000 US gal (91,000 L; 20,000 imp gal) Firebox: ​  • Grate area 150 sq ft (14 m2) Boiler 95 in (2,400 mm) Boiler pressure 300 lbf/in2 (2.1 MPa) Heating surface 5,889 sq ft (547 m2) ​  • Tubes and flues 5,185 sq ft (482 m2)  • Firebox 704 sq ft (65 m2) Superheater: ​  • Type Type E  • Heating area 2,466 sq ft (229 m2) Cylinders 4 Cylinder size 23.75 in × 32 in (603 mm × 813 mm)
Performance figures Maximum speed 80 mph (130 km/h) Power output 5,300–7,000 hp (4,000–5,200 kW) @ 41 mph Tractive effort 135,375 lbf (602.18 kN) Factor of adh. 3.99
Career Operators Union Pacific Railroad Class 4884-1 Numbers 4012 First run 1941 Last run 1959 Retired 1962 Restored May 5, 2021 (cosmetically) Disposition On static display at Steamtown National Historic Site Scranton, PA

Union Pacific 4012 is one of eight preserved Union Pacific Big Boy locomotives. Built in November 1941 by the American Locomotive Company (ALCO) of Schenectady, New York, No. 4012 was retired in 1962 and donated to Steamtown, U.S.A, in Bellows Falls, Vermont, and later moved to Steamtown National Historic Site in Scranton, Pennsylvania, where it remains today.

History

Union Pacific 4012, nicknamed "Big Boy", is a 4-8-8-4 type locomotive built by American Locomotive Company in November 1941. It is among the world's largest steam locomotives. One of 25 built, No. 4012 is one of eight of its type to survive the advent of the diesel era. Referred to as an "articulated" locomotive, because it has more than one set of drivers, Big Boy weighs 1,250,000 pounds (570,000 kg). This locomotive worked for 21 years hauling freight between Cheyenne, Wyoming, and Ogden, Utah, logging over 1,000,000 miles (1,600,000 km) before its retirement in 1962.^[1]

No. 4012 was offered to Steamtown, U.S.A. along with a 4-6-6-4 Challenger and an office car. Steamtown founder F. Nelson Blount, faced with space limitations at Steamtown in 1962, could only accept the 4012.^[2] The Big Boy was on display at Bellows Falls, Vermont, until 1984, when Steamtown moved to Scranton, Pennsylvania.^[1] Since the Steamtown turntable and roundhouse are too small to accommodate the size and weight of 4012,^[1] it has remained outdoors since its arrival at Scranton.^[3]

The Steamtown Special History Study recommended that this locomotive remain at Steamtown because it is the only articulated locomotive in the Steamtown U.S.A. collection and suggested that due to its good condition, 4012 could be restored to working order. However, the study also recommended that 4012 remain on static display, because it is doubtful that the "track, switches, culverts, trestles, bridges, wyes, turntables, and other facilities that would have to carry it to bear its great weight".^[1]

Beginning on October 2, 2019, No. 4012 was removed from public display to begin a cosmetic restoration, including asbestos removal and repainting.^[4][5] The cosmetic restoration was completed on May 5, 2021, and the locomotive was returned to static display for National Train Day.^[6]